Polymers containing carbazole groups

Optically active polymers containing carbazole groups may be synthesised by polymerisation of intrinsically optically active carhazole-containing monomers or by copolymerisation of a variety of optically active co-monomers with nonchiral carbazole-containing monomers. Full details are given and it is concluded that the second method is most useful, not least because it permits a wider variation in polymer backbone structures. V. V. absorption fluorescence emission, NMR, and circular dickroism spectra are reported in detail and help to establish a correlation between photophysical behaviour widi both primary and secondary structural features of the polymers. 

Accordingly for almost a decade the authors have studied, in a systematic way, the synthesis and properties of optically active polymers containing carbazole groups . In the present paper they review and evaluate the relevance of such studies to the interpretation of structural and electronic properties. 

In parallel, Scherf et al. [128] have also reported a ladder-type polymer containing carbazole moieties. Their strategy is quite similar to those presented above the authors copolymerized the carbazole moiety with a phenyl bearing two benzoyl side chains. After the polymerization is completed, the ketone moieties located on the phenyl are reduced into alcohol groups by a reaction with MeLi. The ring-closure reaction of the polyalcohol was carried out by treatment with boron trifluoride etherate, affording the ladder polymer. 

In the effort to make pure blue-emitting materials Shim and coworkers [146] synthesized a series of PPV-based copolymers containing carbazole (polymers 95 and 96) and fluorene (polymers 97 and 98) units via Wittig polycondensation. The use of trimethylsilyl substituents, instead of alkoxy groups, eliminates the electron donor influence of the latter and leads to chain distortion that bathochromically shifts the emission (Amax = 480 nm for 95 and 495 nm for 97). In addition, a very high PLQY was found for these polymers in the solid state (64 and 81%, respectively). Single-layer PLEDs fabricated with 95 and 97 (ITO/polymer/Al) showed EL efficiencies of 13 and 32 times higher than MEH-PPV, respectively (see also Ref. [147] for synthesis and PLED studies of polymers 99 and 100) (Chart 2.20). 

T. Ahn, S. Song, and H. Shim, Highly photoluminescent and blue-green electroluminescent polymers new silyl- and alkoxy-substituted poly(p-phenylene vinylene) related copolymers containing carbazole or fluorene groups, Macromolecules, 33 6764-6771, 2000. 

The absorption and emission of radiation in the near ultraviolet (UV) and visible regions of the electromagnetic spectrum are associated with electronic (and associated vibronic) transitions involving n- and/or n-electron systems of molecules. Synthetic and natural polymers absorb in the UV region and particularly strong absorption spectra are recorded for polymers containing aromatic and heteroaromatic groups (e.g., poly(styrenes), poly(vinyl naphthalenes), poly(vinyl carbazoles)). 

The first group of these polymers contain structures in which a substituent was placed directly on the carbazyl ring. For example, bromine iodine nitroso benzo and iodobenzo were added to the carbazole at various positions, appar-... 

Carbazole polymers can be roughly subdivided into polymers that contain the carbazole group as a pendent group and those that have the carhaz-ole group in the backbone. A special variety is a carbazole polymer with conjugated groups. 

Also, polymers that contain carbazole moieties in the backbone with two acceptor groups as multifunctional chromophores were synthesized. The sytheses were carried out by a Knoevenagel polycondensation of divinylcarbazoles with bis(cyanoacetate)s using 4-(N,N -dimethyl)pyridine as a base. Second-order nonlinear optical properties of the polymers were confirmed by second harmonic generation. The photorefractive optical gain of these polymers was demonstrated to be high. 

Other derivatives obtained from chloromethylated polystyrene include photo-reactive polymers carrying, for example, benzophenone and carbazole groups, polymers for phase-transfer catalysis carrying quaternized graft polyethylenimine chains, and resins containing metal-porphyrins ° and porphyrazines. ... 

Shim et al. recently studied [488] the PL and EL properties of unique blends of poly(2-methoxy-5-(2-ethylhexyloxy)-l, 4-phenylene vinylene] (MEH-PPV) with aklystyryl carbazole group containing poly (methacrylate) (CZ-PMA). These blends showed two isolated PL emissions at 440 and 560 nm corresponding to their component polymers, but only one EL peak, at ca. 580 nm, identical to that of MEH-PPV alone, but with very significantly enhanced intensity. Fig. 12-10 shows some of their data. 

Finally, it is worth noting that optically active polymers containing pendant carbazole units have been prepared by attachment of the carbazole group to chemically activated, optically active macromolecules, such as coisotactic copolymers of chiral a-olefins and p-chloromethyl styrene... 

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